The objectives of this project are to analyze the role of time-domain processing in mediating perception of complex sounds, specifically in relation to periodicity ('pitch') perception. Pitch is a critical dimension of auditory perception in humans; it is important, for example, in the identification, localization, and interpretation of many kinds of sounds, including speech and music. The physiological basis for pitch perception has long been one of the dominant themes in research on hearing, but many questions about the neural extraction of pitch in both the ear and the central auditory pathways remain unanswered. Because pitch perception is so fundamental to hearing, understanding its neural bases will be of value in the development of improved auditory prosthetic devices. Part of the difficulty involved in studying pitch stems from the multiplicity of neural codes available for pitch extraction. In this project, the representation of acoustic parameters influencing pitch perception in humans will be examined in the auditory system of an animal species in which the different neural codes available for periodicity extraction can be separated more readily than in most mammalian auditory systems. Anuran amphibians use pitch-like phenomena for mediating intraspecies communication. The behavioral sensitivity of these animals to acoustic parameters influencing 'pitch' will be examined using both ethologically-based and laboratory-based behavioral techniques. The organization of the anuran inner ear allows separation of place (frequency domain) from temporal (time domain) cues in periodicity extraction. Physiological recordings from the auditory nerve and auditory midbrain of these animals will examine the relative roles of frequency domain and time domain processes in mediating periodicity perception. These data will be used to test hypotheses derived from existing models of 'pitch' extraction, and to develop a computational model of time-domain processing in and anuran auditory system.